Recently, in accordance with rapid growth of electric vehicle market, power storage battery market, mobile smart device market, or the like, the development of a battery such as a lithium rechargeable battery having capacity and output characteristics higher than previously known values, or the like, has been demanded.
In order to develop high capacity battery as described above, generally, an electrode should be thickened, and electrodes should be smoothly transported from the thickened electrode to a current collector. However, carbon black, which is used as a conducting material in an existing rechargeable battery and has a zero-dimensional structure, does not form an effective conducting path, such that carbon black may not satisfy the technical requirements as described above.
Therefore, recently, an attempt to use at least two kinds of conductive carbon-based materials together as the conducting material to further improve characteristics of the conducting material and the electrode has been conducted.
For example, in the case of using at least two kinds of conductive carbon-based materials such as graphene, carbon nano tube, carbon black, or the like, together, each of the conductive carbon-based materials having different structural features may form a point contact, a line contact, and/or a surface contact, thereby making it possible to form a three dimensional network structure. As a representative example, in the case of using graphene and carbon nano tube or carbon black together, the carbon nano tube or carbon black is adsorbed in a surface of the graphene, and a contact is generated between the carbon nano tubes or carbon blacks, such that a three dimensional network structure may be formed. As another example, in the case of using carbon nano tube and carbon black together, the carbon black is adsorbed in a surface of the carbon nano tube, and a contact is generated between the carbon blacks or carbon nano tubes, such that a three dimensional network structure may be formed.
In the case of forming the three dimensional network structure as described above, π-π interactions between the graphenes or carbon nano tubes may be decreased due to steric hindrance. As a result, it is possible to suppress electrical characteristics from being rather decreased by re-aggregation of each of the conductive carbon-based materials in the conductive material.
Due to this advantage, research into a method of preparing a conducting material containing at least two kinds of conductive carbon-based materials in a uniformly dispersed state has been conducted, and several methods as described below have been suggested.
First, as a method of obtaining a powdery composition containing graphene and carbon nano tube together in a uniformly dispersed state, a method of obtaining graphene powder using a Hummers method, acid-treating the graphene powder in an aqueous solvent, mixing the acid-treated graphene powder with carbon nano tube, thermally reducing the mixed powder, dispersing the reduced powder using ultrasonic waves, and recovering a powdery composition using centrifugation, or the like, has been known (J. Mater. Chem., 2011, 21, 2374-2380).
This method has an advantage in that the powdery composition of graphene and carbon nano tube may be obtained in an aqueous solvent, but the entire process was complicated, extremely severe process conditions such as an acid treatment process using a strong acid, or the like, were required, a restacking problem after recovering the powdery composition, or the like, was generated, such that there was a limitation in obtaining the powdery composition in a state in which both components were uniformly dispersed. Therefore, even in the case of obtaining the powdery composition as described above and using the obtained powdery composition as a conducting material of a battery, an effect capable of being obtained by using at least two kinds of conductive carbon-based materials together may not be sufficiently implemented.
As another method known in the art, for example, a method of growing graphene and carbon nano tube through a deposition process such as chemical vapor deposition (CVD) process, or the like, after spin coating a catalyst component on metal foil made of copper, or the like, has been known (Carbon, 2011, 49, 2844-2949).
This method has an advantage in that it is possible to obtain a solid composition of graphene and carbon nano tube while adjusting the solid composition so as to have the desired shape and physical properties. However, since this method is only an experimental method it is difficult to apply this method to a mass production process in industries. Therefore, even in the case of using this method, it is difficult to easily obtain a powdery composition or conducting material in a state in which at least two kinds of conductive carbon-based materials are uniformly dispersed.
Due to problems in the related art, a powdery conducting material composition containing at least two kinds of carbon-based materials in a uniformly dispersed state and a method of preparing the same have been continuously demanded.